High aromatic bromine content is a beneficial quality as it portends enhanced flame retardancy per unit weight of flame retardant. However, a high aromatic bromine content can be accompanied by a higher than desired thermally labile bromine content. The thermally labile bromine content of a brominated flame retardant is determined by measurement of the HBr off-gas generated when the flame retardant is heated to a specific elevated temperature, say 300° C., for a specific period of time. The thermally labile bromine content is dependent on the flame retardant's content of HBr by-product still entrapped in the flame retardant (even after finishing steps to reduce this content) and the amount of molecular, non-aromatic bromine present. An example of non-aromatic bromine are alkyl bromides, wherein the alkyl group is either a bridging group between aromatic groups or is an alkyl substituent on an aromatic group. No matter the source, HBr off-gas from the flame retardant used in the thermoplastic formulations can result in damage to molding equipment used to mold (at elevated temperatures) the thermoplastic formulations into articles, e.g. TV enclosures, etc. Although methods exist for removing HBr by-product entrapped in the flame retardant, the chemically bonded, molecular non-aromatic bromide, is more problematic. There are few options open to the practitioner in this latter case as the techniques used for entrapped HBr reduction are of minimal use against the much more stubborn non-aromatic bromine.
Certain brominated polystyrenes (HP 7010 and HP 3010 flame retardants; Albemarle Corporation) are accepted as commercially significant flame retardants for use in a variety of thermoplastics because of their high aromatic bromine content, low thermally labile bromine content and effectiveness. These commercial products exhibit a thermally labile bromine content of less than about 500 ppm while still providing up to about 68 wt % aromatic bromine in the product.
It would be advantageous if a way could be found of providing relatively low molecular weight, non-polymeric brominated aromatic flame retardants having even higher bromine contents than HP 7010 and HP 3010 flame retardants while at the same time exhibiting thermally labile bromine contents comparable to those achieved in the case of perbrominated diphenylalkanes flame retardants, such as decabromodiphenylethane, and also desirable UV characteristics when compounded with UV stabilizers. It would be particularly advantageous if these results could be achieved along with the provision of a non-polymeric flame retardant having desirable color properties.
This invention is believed to enable the achievement of some, if not all, of these advantages.